MAX II Architecture
Figure 2–7. LE in Normal Mode
sload
sclear
aload
(LAB Wide) (LAB Wide)
(LAB Wide)
Register chain
connection
addnsub (LAB Wide)
ALD/PRE
(1)
Row, column, and
DirectLink routing
ADATA
D
Q
data1
data2
Row, column, and
DirectLink routing
ENA
CLRN
data3
cin (from cout
of previous LE)
4-Input
LUT
clock (LAB Wide)
Local routing
data4
ena (LAB Wide)
aclr (LAB Wide)
LUT chain
connection
Register
chain output
Register Feedback
Note to Figure 2–7:
(1) This signal is only allowed in normal mode if the LE is at the end of an adder/subtractor chain.
Dynamic Arithmetic Mode
The dynamic arithmetic mode is ideal for implementing adders, counters,
accumulators, wide parity functions, and comparators. An LE in dynamic
arithmetic mode uses four 2-input LUTs configurable as a dynamic
adder/subtractor. The first two 2-input LUTs compute two summations
based on a possible carry-in of 1 or 0; the other two LUTs generate carry
outputs for the two chains of the carry-select circuitry. As shown in
Figure 2–8, the LAB carry-in signal selects either the carry-in0or
carry-in1chain. The selected chain’s logic level in turn determines
which parallel sum is generated as a combinational or registered output.
For example, when implementing an adder, the sum output is the
selection of two possible calculated sums:
data1 + data2 + carry in0
or
data1 + data2 + carry-in1
Altera Corporation
March 2008
2–11
MAX II Device Handbook, Volume 1
ALTERA [ ALTERA CORPORATION ]
